The vitamin D endocrine system has been reported to be involved in the regulated of blood pressure and the modulation of vascular structure and function. The investigators have data indicating an inverse relationship between length of time on a high salt diet and plasma 25-hydroxyvitamin D concentration for Dahl salt-sensitive rats. The mean plasma 25- hydroxyvitamin D concentration of salt-sensitive rats fed a low salt diet was more than four-fold higher than that of salt-sensitive rats fed a high salt diet for two weeks. The investigators propose to determine the mechanism and consequences of the reduction of plasma 25-hydroxyvitamin D concentration in salt-induced hypertension. The models for this study will be Dahl salt-sensitive and salt-resistant rats fed high and low salt diets. The specific aims of the proposal are 1) to determine whether the relationship between a high salt diet and plasma 25-hydroxyvitamin D level applies to female, as well as to male, salt-sensitive rats; 20 to determine whether metabolism of 25-hydroxyvitamin D is accelerated in salt-sensitive rats fed a high salt diet; 3) to determine whether vitamin D 25-hydroxylation is altered in salt-sensitive rats on a high salt diet; 4) to compare vitamin D receptor (VDR) levels in the aorta of Dahl salt- sensitive and salt-resistant rats maintained on high and low salt diets; 5) to determine whether synthesis of 1,25-dihydroxyvitamin D by endothelial cells is altered in salt sensitive rats fed a high salt diet. The long-term goals of these studies are to contribute information concerning the etiology of salt-induced hypertension and prevention of the disease. This project has particular relevance to the black American population, because of the higher rat of hypertension and of salt- sensitivity in that population compared with the white American population.